1. Field of the Invention
This invention relates to a method of producing a tubular container integrally with a neck section from a thinly walled tube of thermoplastic resin. It also relates to an apparatus for producing such a container.
2. Background of the Invention
A method of producing a tubular container having a neck section from a parison by blow molding is known. However, the known method has a drawback that the shoulder section of the molded container shows a thick shoulder section because this section is stretched with a low stretch ratio. The wall thickness of the parison has to be finely regulated to overcome this drawback but the operation of such fine regulation is difficult. If the wall thickness of the parison is finely regulated, there arises an additional problem of the difficulty with which a blow nozzle can be introduced into the parison through the neck section when the neck section has a small diameter. Still additionally, there is also a problem that the parting line of the mold halves are transferred to the surface of the blow molded container when the mold is opened. When the parting line is transferred to the surface of the tubular container, it is hardly adapted to printing.
A known method of producing a tubular container proposed to overcome the above identified drawbacks comprises steps introducing a heater into a thinly walled tube and causing hot air to hit the inner wall surface of the thinly walled tube and soften the front end of the thinly walled tube, thereafter discharging hot air through the front end of the thinly walled and heated tube to the outside to make the front end show a conical profile and then forming a neck section by applying a compression molding means from the inside of the thinly walled tube.
However, with this known method, the thinly walled and heated tube is outwardly expanded to deform its appearance when hot air is discharged from the inside of the tube because no measures are taken to prevent such deformation of the thinly walled tube and hot air is made to flow toward the inner wall surface of the tube and away from the neck forming section.
With this known technique, therefore, the producing efficiency is reduced particularly when the thinly walled tube is externally heat treated to gather resin to the front end of the thinly walled tube in order to produce a neck section there because the front end of the thinly walled tube can be introduced into an external heater only with difficulty. Additionally, unnecessary portions of the thinly walled tube can be heated and deformed because the area of the outer wall surface of the thinly walled tube to which hot air is discharged is not accurately defined. The net result will be a tubular container having a disproportionately thick shoulder section due to the large volume of softened resin gathered to produce the neck section or a deformed container having poor commercial value. Another problem is that the neck section cannot be produced after the surface of the tubular container is subjected to a printing process if the thinly walled tube has been deformed.